The present invention relates to a liquid crystalline polyester easy to fix its liquid crystal orientation in glass phase, exhibiting a large wavelength dispersion of birefringence and suitable for the application to an optical element.
Recently, as to liquid crystalline polymers, research and development have been made actively in the field of high-performance materials utilizing high heat resistance and moldability or in the field of functional materials utilizing changes in liquid crystal structure caused by heat or by an eternal field such as an electric field and also utilizing the fixing of phase. Particularly, in the field of high-performance materials, commercialization has already been achieved. On the other hand, in the field of functional materials, although research has actively been directed towards attaining the application of such polymers in optical recording, non-linear optical materials, alignment films for crystals, optical fibers and optical elements for liquid crystal displays, commercialization has not been achieved yet. In the case of application of liquid crystalline polymers to functional materials, the application can be broadly classified into one which utilizes a dynamic change in phase transition of liquid crystal and one in which a molecular orientation peculiar to liquid crystal is fixed for utilization as a static element. In both such applications, most uses employ optical properties of liquid crystal. In connection with the latter application just mentioned above, as important conditions required for liquid crystalline polymers capable of being fixed their liquid crystal orientations and applicable to optical elements, there are mentioned conditions such that the fixing of liquid crystal orientation should be easy, the liquid crystal orientation after fixing should be stable, and optical properties such as refractive index, birefringence and wavelength dispersion should be freely controllable. Particularly, if an optical element exhibiting a large wavelength dispersion of birefringence, for which there has been a great demand recently in the display field, can be produced using a liquid crystalline polymer, it becomes possible to obtain an epoch-making optical element in combination with properties for polarized light peculiar to a fixed structure of liquid crystal orientation.
However, a liquid crystalline polymer exhibiting a large wavelength dispersion of birefringence and capable of being fixed its liquid crystal orientation stably and hence capable of being used as the material of such optical element as just mentioned above, has not been developed yet, nor has there been made scarcely any research.
It is the object of the present invention to solve the above-mentioned problem of the prior art.